Means for securing interchangeability



Feb. 29, 1944. l Q E. slmpsQN 2,342,703

MEANS FORl SECURING INTERCHANGEABILITY Filed May 6, 1942 Figl-Elnrel-LEE E. Eximpann Patented Feb. 29, 1944 Ul-TED STES ,ser OFFICEMEANS ron snoUmNG INTERCHANGE- ABILITY (Grantedunder the act oi March 3,1883, as amended April 30,1928; 370 0. G. 757)- 3 Claims.

The invention described herein may be manuiactured and used by or forthe Government for governmental purposes, without the payment to me ofany royalty thereon.

This invention relates to means for securing interchangeability of theparts of a firearm with particular reference to obtaining the properheadspace for the firearm.

Inherent in rearms having fixed barrels with breech mechanisms that lockaganist a ixed part of the receiver is the diiculty of obtaining theproper spacing between the face of the bolt and the cartridge, which isgenerally referred to as headspace. Due to wear of tools manufacturingtolerances are provided on all dimensions of the various components ofthe rearm as well as other tolerances that govern fit of the components.It may thus be readily seen that even amongst a number of similarcomponents corresponding dimensions can vary slightly and for examplesome of these pieces will be longer or shorter than others. In theassembly of new rifles, it is frequently impossible to obtain the properheadspace because the accumulation of tolerances in componentscomprising the breech mechanism are such that the bolt face will notposition for correct headspacing. Then only by laborious selectiveassembly and repeated trial can the proper headspace conditions beobtanied.

The locking surfaces of firearms which have been subjected to prolongedfiring stretch and Wear from the constant pounding of repeatedexplosions. This often increases the headspace to such an extent thatWhatever combination of new breech mechanism components are placed inthe firearm the correct headspace cannot be obtained. It then becomesnecessary to replace these components or institute a major overhaul toobtain the correct headspace in order to restore the rearm to itsoriginal useful condition.

It is an object of this invention to provide a variable means forobtaining interchangeability of any combination of components of thebreech mechanism of a rearm.

Another object of this invention is to provide a ready means foreffectively restoring the headspace of used and Worn firearms.

It is a particular object of this invention to provide adjustableheadspace means for a firearm such as disclosed in U. S. Patent No.1,293,022 to John M. Browning.

The specific nature of the invention as Well as other objects andadvantages thereof will clearly appear from a description of a preferredembodiment as shown -in the accompanying drawing in which:

Fig. 1 is a partial View in axial section of the breeching mechanism oia lrearm.

Fig. 2 is a perspective view of the headspace adjusting plate.

In Fig. 1 is shown in section the -breeching mechanism of a firearm,such as shown in U. S. Patent No. 1,293,022 to John M. Browning, in itsclosed or locked position within the receiver i, which is also shown insection. The breeching mechanism comprises mainly the bolt 2, the boltlock the link and the slide 5. With the breech mechanism inthe positionshown, the bolt lool: 3 engages the shoulder 5 on the receiver l and inthis position will resist the rearward force of the gases against thebolt 2 when a cartridge I is iired.

To properly support the head of the cartridge "l, the face 3 of bolt 2must at all times engage or very nearly engage the face of the cartridgel. The space between the head of the cartridge, or some convenientreference point in the chamber, and the face of the bolt is known as theheadspace. It is necessary that when the bearing surface 9 of the 'boltlock 3 snugly engages the shoulder of receiver I the bolt face 8 iswithin prescribed headspace limits to prevent ruptured or blown offcartridge heads with resultant dangel-ous escapage of gas.

As previously pointed out, due to allowable manufacturing tolerances itis possible under some conditions to have certain components orcombinations of components, which comprise the breech mechanism, be ofsuch length that the bolt face 8 Will not come within prescribedheadspace limits. Such a condition exists when a bolt lock 3 and a bolt2 of minimum length, joined together by a pin I2 of maximum diameter,are assembled to a receiver i in which the shoulder E is the maximumdistance from the end I3 of receiver I, and when the shoulder I4 ofchamber 'I is a maximum distance from end I3 of receiver i. Thus, underthe condition of maximum and minimum tolerances just described, the boltface 8 will not be suiciently forward to be Within the headspacetolerances. As it is extremely inconvenient, and laborious, and often attimes unvavailing, to obtain the proper headspace by selective assemblyof the aiected components, a convenient means for adjustably obtainingthe headspace without the need for selective assembly is provided.

A dovetailed slot l@ is provided in the bolt lock 3. In the slot IiI aheadspace adjusting plate I I (Fig. 2) is slidably inserted and securelyheld by the slot Ill. The plate H is then locked in place by the stakeI6 in stake slot I5 or by other suitable means. It should be understoodthat this locking means should not permanently fasten the plate H to thebolt lock 3 but only securely enough to prevent its loosening duringoperation of the gun as it may be necessary to remove the plate l l asWill be presently shown.

By providing the headspace adjusting plates l I in a Wide variety ofslightly diiering thicknesses, it is possible to-obtain any headspaceadjustment desired Whichiwill satisfy tolerance requirements despite anaccumulation of tolerances that without the headspace adjusting plate Ilwould have caused the rejection of the components.

Firearms that have been subjected to severe ring frequently developexcessive headspace which cannot be corrected without replacement ofcomponents. Such firearms may be conveniently and inexpensively restoredto their original usefulness by provision of the slot Ell and the platel I as described. At any time a rearm embodying this invention is firedto such an extent as to increase the headspace beyond the prescribedlimits, it.is only necessary to replace the headspace adjusting plate Hwith a thicker plate to correct this condition.

It should be understood that the method described can be applied torearms other than the one illustrated in the drawing and is thereforeapplicable to any rearm with a i'lxed barrel and Va breech mechanismthat locks against a xed part of the receiver.

I claim:

1. In a firearm having a xed receiver, a bolt and a. barrel, a boltlocking assembly comprising a xed locking surface in said receiver, apivoted member on said bolt having a surface adjacent to said receiversurface in the locked position of said. pivoted member, the improvementcomprising a slot in said pivoted member surface, a locking membersecured in said slot and having a surface in engagement with saidreceiver locking surface in the locked position of said pivoted member,the thickness of said locking member being selected to obtain properheadspace.

2. In a rearm having a receiver, a barrel, a movable bolt in saidreceiver, and a bolt locking assemblsr comprising al xed locking surfacein said receiver and a pivoted member on said bolt having a surfaceadjacent to said receiver surface in the locked position of said pivotedmember, the improvement comprising a separate insert in said pivotedmember positioned for engagement with said locking surface in thelocking position of said pivoted member, said insert protruding beyondthe surface of said pivoted member in accordance with the headspacerequirements of said rearm.

3. In a firearm as in claim 2, removable fastem ing means for saidinsert whereby inserts of different sizes may be readily interchanged.

CLARENCE E. SIMPSON.

